The proliferation of smartphones and other wireless devices has led to the ever-increasing demand for wireless spectrum. In an effort to ameliorate this problem, the U.S. Federal Communications Commission (“FCC”) has opened up the 3550-3700 MHz band (“3.5 GHz band”), which has traditionally been reserved for military use, for shared-spectrum use. Shared-spectrum use has also been contemplated for the 1695-1710 MHz, 175-51780 MHz, and 2155-2180 MHz bands (collectively, the “AWS-3” bands) during a transitional period when federal incumbent systems relocate out of the bands. When spectrum is shared, some mechanism must be adopted to ensure users of the same spectrum do not interfere with each other and users with higher priorities are guaranteed access to the spectrum in a situation of a conflict.
Using the 3.5 GHz band as an example, to protect existing users of the band, a three-tiered model has been adopted by the FCC, as illustrated in FIG. 1. As shown in the figure, incumbent access (IA) users, shown as federal and non-federal incumbent systems, are positioned at the top tier and have the highest priority. One or more Spectrum Access Systems (“SASs”) may facilitate spectrum sharing between the incumbent users and public users, such as commercial cellular operators, emergency vehicles, police, etc. Among the public users, some may obtain higher priority under a Priority Access License (“PAL”), while others may operate under General Authorized Access (“GAA”), i.e., without a license, but with the lowest priority. A spectrum access system (“SAS”) may facilitate the three-tiered model by ensuring that devices in a lower-priority access tier do not interfere with those in a higher-priority tier. The SAS may accomplish this by monitoring interference and dynamically assigning frequency bands to devices operating in the shared spectrum. It will be understood that a “frequency” may be a frequency band, a frequency channel, or a channel, and vice versa.
The public use devices, i.e., the PAL and GAA devices, may each operate or run a communications system and communicate with end user devices, such as smartphones or other portable devices carried by end users, via any suitable wireless communication technologies or standard protocols, such as Long Term Evolution (LTE), Wideband Code Division Multiple Access (WCDMA), Global System for Mobile Communications (GSM), etc. The SAS coordinates and manages spectrum sharing among the incumbents, the PAL systems, and the GAA systems, by assigning spectrum to the PAL and GAA devices as requested for use by the respective systems, while at the same time ensuring that the PAL and GAA devices and systems do not interfere with the incumbents, that the GAA systems do not interfere with the incumbents and the PAL systems, and that the PAL users do not interfere with each other.
When the systems are in close proximity with one another, functions of the SAS alone may be insufficient to avoid harmful interference. Assistance from the individual systems may be necessary to ensure interference stays at a permissible level.